In recent years, the Thin Film Transistor-LCD (TFT-LCD) has been rapidly developed and applied widely. Most of the liquid crystal displays on the present market are back light type liquid crystal display devices, which comprise a liquid crystal display panel and a back light module. Generally, the liquid crystal display panel comprises a Color Filter (CF) substrate, a Thin Film Transistor (TFT) substrate, Liquid Crystal (LC) sandwiched between the CF substrate and TFT substrate and sealant. The working principle is that the light of backlight module is reflected to generate images by applying driving voltages to the two glass substrate for controlling the rotations of the liquid crystal molecules.
In the liquid crystal display devices of prior art, the white light emitting diodes (Light Emitting Diode, LED) are generally used as a backlight. The most common white LED is a LED with the blue light emitting chip (B chip) plus yellow phosphor (Y phosphor). As the LEDs using the yellow phosphor is employed to be a backlight within a liquid crystal display panel, the display's color saturation is generally relatively lower (the NTSC color gamut value is generally 72%), the color is not bright enough. In order to improve the color saturation and to achieve more vivid color performance, the yellow phosphor is mainly changed to red green (RG) phosphor at present, for having the white LED with blue light emitting chip plus red green phosphor. However, compared to the yellow phosphor, such arrangement can only increase about 25% of the color gamut (the NTSC color gamut value is generally 90%), which still cannot meet the new BT.2020 color gamut standard (equivalent to the NTSC color gamut value of 134%). At present, the technology using the quantum dots (Quantum Dot, QD) material with a narrow emission spectrum is the technology, which is the easiest to implement and the most energy efficient technology within the technologies able to achieve 80% BT.2020 color gamut standard now.
The quantum dots, also known as nanocrystals are nanoparticles, of which the particle sizes are generally between 1-10 nm, and due to the quantum confinement of the electrons and the holes, the continuous band structure becomes a discrete level structure having a molecular characteristic, and can be excited to emit fluorescence. The emission spectrum of the quantum dots can be controlled by changing the size of the quantum dots. By changing the size of the quantum dots and the chemical composition thereof, the emission spectrum can cover the entire visible region, and includes a wide excitation spectrum and a narrow emission spectrum, and thus the spectral coverage rate is higher. Moreover, compared with the fluorescence lifetime of the organic phosphor, the fluorescence lifetime of quantum dots is 3-5 times to have a good light stability. In short, the quantum dots are an ideal fluorescent material.
The quantum dot mixed material packaged in the LED bracket as a fluorescent luminescent material and silica gel is named as a quantum dot light emitting diode (QLED). However, the quantum dots are sensitive to water and oxygen, and the fluorescence efficiency will be irreversibly decreased as being exposed in the environment of water and oxygen. Therefore, the package of quantum dots needs to have a good water and oxygen insulation ability. In addition, as the temperature rise, the luminous efficiency of the quantum dot material will gradually decline, and the emission wavelength will be red shifted, so the quantum dot package needs to be able to insulate the high temperature or to have a better heat dissipation environment. At present, in the quantum dot LED backlight applications, the main package for the quantum dots is to package the quantum dots in the glass tube or in the water/oxygen-insulated polyethylene terephthalate (PET) film. However, the former uses the glass, and there are drawbacks of fragile, low light utilization, difficulty to achieve narrow border, while there are drawbacks of easily producing the blue light color shift of the backlight edge and high cost in the latter.